Display screen or portion thereof with transitional graphical user interface



FIG. 1 is the first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing my new design;

FIG. 2 is the second image thereof;

FIG. 3 is the third image thereof; and,

FIG. 4 is the fourth image thereof.

The outer broken lines in the figures depict a display screen or portion thereof and form no part of the claimed design. The remaining broken lines in the figures depict portions of the transitional graphical user interface that form no part of the claimed design.

The appearance of the graphical user interface sequentially transitions between the images shown in FIGS. 1-4. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM I claim the ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 